Is it possible to change shipping options after a bid has been made?

[echidnite]

I realised I set an auction to ship 'worldwide' instead of picking individual countries (UK, North America, etc) and I realised this opens me up to bids from countries with problematic postal systems like Russia. 

Is there a way to change this option once a bid has already been made? Assuming I will not change the shipping option to affect the current bidder, but just to add some exclusions.